Volume 12, Issue 22, Pages 1908-1918 (November 2002) Caenorhabditis elegans HUS-1 Is a DNA Damage Checkpoint Protein Required for Genome Stability and EGL-1-Mediated Apoptosis  E.Randal Hofmann, Stuart Milstein, Simon J. Boulton, Mianjia Ye, Jen J. Hofmann, Lilli Stergiou, Anton Gartner, Marc Vidal, Michael O. Hengartner  Current Biology  Volume 12, Issue 22, Pages 1908-1918 (November 2002) DOI: 10.1016/S0960-9822(02)01262-9

Figure 1 Identification of hus-1 Mutants (A) Genetic map and genomic structure of the hus-1 gene. Boxes represent coding sequence. The position and nature of the hus-1 mutations are indicated. (B) Quantification of cell proliferation arrest in wild-type, hus-1(op241), and hus-1(op241);unc-119(ed3) strains with integrated (opIs34) and nonintegrated (opEx566) transgenic constructs. The number of cells in the proliferating region of the germline was viewed by DIC and scored 50 μm from the distal end of the gonad 12 hr following irradiation, as described in Supplementary Experimental Procedures. Each bar represents five worms ± SD. (C) Comparison of the germline apoptotic response to irradiation between wild-type and hus-1 mutants. Corpses were scored in the distal arm of the gonad of adult animals following indicated doses of irradiation. hus-1 deletion mutants are completely defective for DNA damage-induced apoptosis; however, physiological germ cell death is present. Current Biology 2002 12, 1908-1918DOI: (10.1016/S0960-9822(02)01262-9)

Figure 2 HUS-1(G99D) Is Defective for MRT-2 and PDI-2 Binding (A) Using the Blosum62mt2 matrix (Align-X), the alignment of the putative helical Rad9 interacting region of Hus1 from human, mouse, fly, worm, and fission yeast and Mec3 from budding yeast was determined. The affected residue in op241 is indicated by an arrowhead. See text for details. (B) The yeast two-hybrid system was used to test for protein interactions with wild-type (WT) and mutant (G99D) HUS-1-GAL4 DNA binding domain (DB) fusions by scoring for LacZ expression and growth on −Ura plates (no selection: −Leu −Trp). HUS-1(WT) interacts with GAL4 activation (AD) fusions of MRT-2, K12H4.1, F56D12.5, and PDI-2. HUS-1(G99D) does not interact with MRT-2 and PDI-2, but it still interacts with K12H4.1 and F56D12.5. (C) In vitro interaction of HUS-1 and MRT-2. GST-HUS-1(WT), but not GST-HUS-1(G99D) or GST alone, interacts with Myc-epitope-tagged MRT-2 (lanes 1–3). GST-MRT-2 is able to interact with wild-type (WT) but not mutant Myc-epitope-tagged HUS-1(G99D) (lanes 4 and 5). Current Biology 2002 12, 1908-1918DOI: (10.1016/S0960-9822(02)01262-9)

Figure 3 HUS-1 Nuclear Localization Requires MRT-2 and HPR-9 (A) Fluorescent microscopy of integrated transgenic strains expressing fusion constructs in gonads and embryos of wild-type, mrt-2(e2663), and rad-5(mn159) mutant backgrounds. The genotype and construct used are indicated, and expression is shown in the indicated stage of oogenesis and early embryos. pRH21 is a full-length translational fusion containing 2252 bp of genomic sequence 5′ to the stop codon. (B) Fluorescent microscopy of 4-cell-stage embryos from F2-integrated transgenic worms fed dsRNA produced from indicated genes as described in the Experimental Procedures. For confirmation of ced-3(RNAi) and hpr-17(RNAi), germ cell death and hypersensitivity to radiation-induced embryonic lethality, respectively, were scored. The scale bars represent 10 μm. Current Biology 2002 12, 1908-1918DOI: (10.1016/S0960-9822(02)01262-9)

Figure 4 Subcellular Relocalization of HUS-1::GFP following DNA Damage (A) Fluorescent microscopy of proliferating germ cells expressing HUS-1::GFP (opIs34). Irradiated worms (opIs34 = 100 Gy; rad-5(mn159);opIs34 = 10 Gy) were viewed 8 hr following irradiation. HUS-1::GFP is diffuse in controls. Relocalized HUS-1::GFP is seen as bright foci. The scale bar represents 5 μm. (B) Quantification of HUS-1::GFP foci in wild-type and rad-5(mn159) backgrounds. Foci were scored in 40 proliferating germ cells in a single Z stack following mild doses of X-rays at indicated times. Each bar represents ten worms ± SEM. (C) Colocalization of HUS-1::GFP with chromatin following exposure to ionizing radiation. The top panel shows proliferating germ cells. The bottom panel shows a single oocyte nucleus in diakinesis. Arrowheads point to two DAPI-stained bivalents from an oocyte in diakinesis. The scale bar represents 2 μm. (D) Fluorescent microscopy of meiotic germ cells from worms fed dsRNA from rad-51 and a par-1 control. As in (C), HUS-1::GFP foci overlap with chromatin stained with Hoechst 33342 dye. The scale bar represents 5 μm. Current Biology 2002 12, 1908-1918DOI: (10.1016/S0960-9822(02)01262-9)

Figure 5 hus-1 Deletion Mutants Show a Telomere Maintenance Defect and a High Rate of Spontaneous Mutations (A) Southern blots were performed with a C. elegans telomere-specific probe on genomic DNA from wild-type (WT) and indicated inbred generations of op244 after outcrossing. (B) Oocytes in diakinesis were stained with DAPI from wild-type and late-generation hus-1(op244) mutants that no longer produced viable progeny. Wild-type oocytes contain six easily visible bivalents, while late-generation hus-1(op244) mutants often have only 3–5 visible bivalents. The scale bar represents 2 μm. (C) Spontaneous unc-93(e1500) reversion frequencies (log) in hus-1(+) and two independently generated hus(op244) strains (F1.1 and F1.2). The unc-93(e1500) gain-of-function mutation results in severe paralysis that can be suppressed by loss of function of any one of five different genes; this loss of function includes inactivating second site mutations within the unc-93 gene itself [47]. Current Biology 2002 12, 1908-1918DOI: (10.1016/S0960-9822(02)01262-9)

Figure 6 egl-1 Is Transcriptionally Induced by Irradiation in a hus-1- and cep-1-Dependent Manner (A) Northern blots were performed with 2 μg polyA-enriched RNA isolated from wild-type and hus-1(op244) mutant young adult worms at indicated times after exposure to 120 Gy γ-irradiation. The same blot was reprobed with a PCR-generated probe from the indicated gene on the left. (B) Average fold induction of egl-1 gene expression in wild-type, hus-1(op244), cep-1(w40), cep-1(gk138), and glp-4(bn2) mutants after 100 Gy X-ray irradiation as determined by real-time quantitative RT-PCR. glp-4(bn2) worms were grown at the nonpermissive temperature, and 90–100 worms were selected that lacked a germline. Each bar represents the average ± SD. (C) Induction of egl-1::gfp expression in the germline. A construct containing 2.7 kb of genomic sequence 5′ to the translation start site of egl-1 fused to GFP equipped with two nuclear localization signals. Worms were synchronized and irradiated as L4 animals. GFP expression was analyzed in dissected gonads 30 hr following irradiation. Expression was seen in both proliferating and late-pachytene germ cells in most (12/16) irradiated animals. Background expression could be seen in the late-pachytene germ cells in few (2/23) nonirradiated controls, but not (0/23) in the proliferating germ cells. The arrowhead indicates the distal end of the gonad. The scale bar represents 10 μm. Current Biology 2002 12, 1908-1918DOI: (10.1016/S0960-9822(02)01262-9)

Figure 7 Model: A Pathway for DNA Damage-Induced Apoptosis and Cell Cycle Arrest in C. elegans DNA damage recruitment of the HUS-1/MRT-2/HPR-9 complex to the site of the lesion, where it activates cell cycle arrest of proliferating stem cells. This complex also signals to the apoptotic machinery via CEP-1-dependent upregulation of egl-1. Current Biology 2002 12, 1908-1918DOI: (10.1016/S0960-9822(02)01262-9)